Continuously variable transmission and variants

ABSTRACT

The present invention pertains to the field of machine-tooling and essentially relates to a continuously variable transmission that comprises a central shaft ( 1 ), an epicycle ( 5 ) having outer central discs ( 4 ) attached thereon, solar wheels in the form of inner central discs ( 2 ), a carrier ( 6 ), a plurality of intermediate friction discs ( 3 ) mounted in the support ( 6 ) using axes ( 7 ) as well as rotating levers ( 12 ) and a mechanism for the combined modification of the transmission ratio and of the pressure. The latter includes power members applying an axial action ( 11 ) which are arranged on the end sides of all the above-mentioned central friction discs ( 2, 4 ), or else members pressing on the rotating levers as well as power members applying an axial action which are arranged on the outer side of the central friction discs so as to ensure contact in predetermined annular areas. The average axial rigidity of the power members applying an axial action and brought into contact with the central outer friction discs is, in terms of absolute value, higher than the average rigidity of the power members applying an axial action and brought into contact with the central inner friction discs ( 2 ).

FIELD OF INVENTION

The present invention relates to the field of machine-building and, inparticular, to a continuously variable transmission and may be used invarious fields of technology in cases where it is necessary to ensurecontinuously variable torque transmission while adjusting thetransmission ratio depending on a load at the transmission output. Itmay be used, in particular, for means of transportation andvariable-speed drive units.

PRIOR ART

At present, continuously variable transmissions made on the basis of afriction variable-speed drive are of wide use.

Known in the art is a planetary friction variable-speed drive comprisingthe outer central friction discs and the intermediate conical frictiondiscs as well as the pressure members that apply an axial action to thecentral friction discs and the intermediate conical discs arrangedtherebetween, a radial movement of the intermediate discs and associatedchange in the transmission ratio of the variable-speed drive takingplace due to applying an axial action to the said discs. Thus, thepressure members are at the same time mechanisms changing thetransmission ratio. GB Patent 1384679, IPC⁶ F16H 15/50, 1975.

The closest to the claimed solution under the first variant as to thetechnical substance and achieved result is a continuously variabletransmission comprising a planetary friction variable-speed driveconsisting of the inner and outer central friction discs laterallyembracing the intermediate friction discs, a mechanism for combinedmodification of the transmission ratio and of the pressure made in theform of rotating levers carrying the intermediate friction discs andarranged on the planetary variable-speed drive carrier with thepossibility of changing the position of the rotating levers. Patent RF2091638 IPC⁶ F16H 15/52, 1997 (the prototype). In the known solution themechanisms for combined modification of the transmission ratio and ofthe pressure press the central friction discs to the intermediate discswith forces proportional to transmitted torques, subject to pre-pressingby springs.

The prototype transmission has several inherent deficiencies, namely:

the pressure members of the mechanism for combined modification of thetransmission ratio and pressure are complex, and, what is mostimportant, they do not solve the task of optimal pressing the discs toeach other due to the fact that the friction coefficient at the pointsof the friction oil contact is varied greatly; according to the resultsof the study performed by the author the value of this coefficient forthe central inner friction discs is varied in the range from 0.015 to0.03 and for outer ones

from 0.02 to 0.08; therefore the pressure, which is proportional to thetorque only, does not achieve the required result in the planetarysystems;

the systems of pressure members of the said mechanisms, includingautomatic adjustment with pre-pressing by a spring with a force that isusually corresponds to 25-35% of the maximum force, also do not achievethe required result; there the initial working adjustment for an outercentral friction disc should be app. 5-7% of the maximum force, and eventhat, the most complex, combined system creates the pressure 5 timesgreater than the necessary one and leads to a sharp reduction in theefficiency, but for a car transmission this working mode is most widelyused, especially when moving along a road (at the highest transmission);

the friction coefficient depends heavily on the rotation speed of thevariable-speed drive shafts, and the above pressure members system donot enable to correct it.

The closest to the claimed solution under the second variant as to thetechnical substance and achieved result is a continuously variabletransmission comprising a planetary friction variable-speed driveconsisting of the inner and outer central friction discs laterallyembracing the intermediate friction discs, a mechanism for combinedmodification of the transmission ratio and of the pressure made in theform of rotating levers carrying the intermediate friction discs andarranged on the planetary variable-speed drive carrier with thepossibility of changing the position of the rotating levers by pushersmoved along guides. Patent RF 2091637 IPC⁶ F16H 15/52, 1997 (theprototype).

A specific feature of the invention according to the prototype is thatthe pushers are spring-loaded to the guides by centrifugal forcescreated due to the unbalanced state of the rotating levers relative totheir rotation. Such implementation creates very inconvenient conditionsof loading the pushers, resulting in inaccuracy and low reliability ofregulation. For example, given the rotation speed of a low-speed shaftis changed tenfold (this is the real range of a variable-speed drivetransmission-ratio variation), the centrifugal force varies hundredfold,the torque “exerting a counter-action” to that force in the regulationsystem varies approximately tenfold, and the maximum torque, which on alow-speed shaft corresponds to the minimum rotation speed, will justcorrespond to the minimum centrifugal force. Practical studies haveshowed that such a system does not ensure the necessary accuracy of thetransmission-ratio regulation.

DESCRIPTION OF THE INVENTION

The objective of this invention is to create a continuously variabletransmission on the basis of a variable-speed friction disc drive havinga higher efficiency, durability, reliability and convenient in operationdue to simplifying the design of the mechanism for combined modificationof the transmission ratio and pressure, ensuring compliance of thefriction discs pressure force in different operation modes with thetransmission ratio value as well as due to dependence of thevariable-speed drive transmission ratio on the output shaft load.

According to the first variant, in order to achieve the said technicalresult in a known continuously variable transmission comprising aplanetary friction variable-speed drive consisting of the inner andouter central friction discs laterally embracing the intermediatefriction discs, a mechanism for combined modification of thetransmission ratio and of the pressure made in the form of rotatinglevers carrying the intermediate friction discs and arranged on theplanetary variable-speed drive carrier with the possibility of changingtheir position, the mechanism for combined modification of thetransmission ratio and of the pressure is provided with power membersapplying an axial action, which are arranged on the end sides of theinner and outer central friction discs so as to ensure their contact inthe annular areas opposite to the annular areas of contact between theinner and outer central friction discs and the intermediate frictiondiscs, an average axial rigidity of the power members applying an axialaction, which are brought into contact with the outer central frictiondiscs, is made so as to be higher, in terms of absolute value, than anaverage axial rigidity of the power members applying an axial action,which are brought into contact with the inner central friction discs.

Some other embodiments of the first variant of this invention arepossible, according to which it is advisable that:

a mechanism for combined modification of the transmission ratio and thepressure would be provided with support members arranged on the centralshaft and on the epicycle on the rear side of the power members applyingan axial action and made with the stops contacting the power membersapplying an axial action with the possibility of varying their axialrigidity both in magnitude and in negative/positive value;

each power member applying an axial action, as included in the mechanismfor combined modification of the transmission ratio and the pressure,would be made in the form of a chamber communicating with thepressurized working medium and arranged on an epicycle with thepossibility of pressing of, at least, one outer central friction disc tothe respective intermediate friction discs depending on the workingmedium pressure in the said chamber;

each power member applying an axial action would be made in the form ofan annular conical surface made on a power member arranged on thecentral shaft and on an annular conical surface facing it and made on aninner central friction disc, between the said annular conical surfacesweights being arranged with the possibility of their radial movementalong a conical gap formed by the said annular conical surfaces and withthe possibility of varying the value of pressing the inner centralfriction discs to the intermediate friction discs;

the said weights would be made in the form of shaped spring rings withalternating radial slots.

The said features are essential and interrelated therebetween bycause-effect relation with the formation of a totality of essentialfeatures sufficient for achieving the technical result.

This is ensured by the fact that the central friction discs, both theinner and the outer ones, are pressed to the intermediate friction discsby the power members applying an axial action, in particular by springsmade in the form of well-known plate or cantilever beam discs arrangedon either side of the intermediate friction discs both on the outer andthe inner central friction discs. The said springs interact with thesaid discs on the back surfaces at the radii that are closer to theraces than to the disc bases.

The inner and outer central friction discs themselves may serve as suchsprings, in such a case the average, over the total travel, rigidityvalue of the springs of the outer central friction discs in terms ofabsolute value (since such value may be varied from positive values tozero and further to negative values) is higher than the similarparameter of the springs of the inner central friction discs. Therigidity of the springs of the outer or inner central friction discs maybe varied in their travel smoothly or discretely, and the said springsmay contact by their face or back surfaces with the stops or othersprings with the possibility of varying the rigidity of the firstsprings of the inner and outer central friction discs. In order tocorrect the force of pressing the inner and outer central friction discsto the intermediate friction discs, the continuously variabletransmission is provided with pressure adjusters acting according to therotation speed and made in one variant of this invention in the form ofweights arranged between the annular conical surfaces made on thesupport members and on the inner central friction discs and installedwith the possibility of increasing the pressure force while the rotationspeed is increased, as well as in the form of chambers for supplying thepressurized working medium (e.g., gas or liquid), which also increasesthe pressure force, maintaining it at a required level.

Thus, the optimal, as to the efficiency, pressing the outer and innercentral friction discs to the intermediate friction discs is ensured,which is conditioned, e.g., by the fact that the torque, in particularthat developed by car engines in the full fueling mode withoutenrichment (the most economical mode in which a continuously variabletransmission should work), is close to a constant value, and the torqueon the carrier of a variable-speed drive (output torque) depends on thevariable-speed drive transmission ratio that is rather accuratelyrelated to the radial movement of the axle of the intermediate frictiondiscs, and, therefore, to the axial travel of the spring. Thus, eachmovement of the intermediate friction discs corresponds, due to acertain change in the spring position, a well-defined optimal pressureforce slightly distorted by a change in the rotation speed. Such achange, which results in some insignificant change of the frictioncoefficient, may be corrected with the adjusters introduced into thecontinuously variable transmission, such adjusters having centrifugalweights or pressure chambers creating an additional pressure force.

The engine of a transportation vehicle works under low fueling,according to modern methods of automatic control of the car power unitwith the known continuously variable transmission, only at the start andat low movement speeds. In those modes the variable-speed driveefficiency, according to calculations and experiments, is reduced notmore than by 1-3% due to a non-optimal pressure force (overpressure),which is not likely to be noticed compared to a far more noticeablereduction in the engine efficiency under low fueling. The efficiency ofthe claimed continuously variable transmission with the proposed systemof exerting elastic pressure on the friction discs is most applicablefor variable-speed drives according to the given system and reaches0.96-0.97 at the highest transmission ratios of 1.2-1.3.

According to the second variant, in order to achieve the said technicalresult in the known continuously variable transmission comprising aplanetary friction variable-speed drive consisting of the inner andouter central friction discs laterally embracing the intermediatefriction discs, a mechanism for combined modification of thetransmission ratio and of the pressure made in the form of rotatinglevers carrying the intermediate friction discs and arranged on theplanetary variable-speed drive carrier with the possibility of changingtheir position, a mechanism for combined modification of thetransmission ratio and of the pressure is provided with pushers arrangedwith the possibility of moving along the guides, members applyingpressure to the rotating levers and power members applying an axialaction arranged on the face sides of the inner and outer centralfriction discs so as to ensure their contact in the annular areasopposite to the annular areas of contact between the inner and outercentral friction discs and the intermediate friction discs, an averageaxial rigidity of the power members applying an axial action, which arebrought into contact with the outer central friction discs, is made soas to be higher, in terms of absolute value, than an average axialrigidity of the power members applying an axial action, which arebrought into contact with the inner central friction discs, and the saidpressure members being connected to the rotating levers with thepossibility of ensuring the rotation of the said levers to the sidecorresponding to the reduction in the transmission ratio from thecentral shaft to the low-speed shaft.

Some other embodiments of the second variant of this invention arepossible, according to which it is advisable that:

the transmission would be provided with a driven mechanism connectingthe carrier with the low-speed shaft and made, in particular, as adriven jaw clutch;

the guides would be made as helical profiled surfaces, which directionwould ensure, if the carrier advances the low-speed shaft in case ofmaking the central shaft the driving one and making the low-speed shaftthe driven one, an angular movement of the rotating levers to the sidecorresponding to an increase of the transmission ratio;

the pressure members of the rotating levers would be made as, at least,one spring connected on one its end to the carrier and on the other endto the low-speed shaft;

the pressure members of the rotating levers would be made as, at least,one spring connected on one its end to the low-speed shaft and on theother end to the rotating levers having the capacity of moving angularlywith respect to the carrier;

the pressure members of the rotating levers would be made as, at least,one spring connected on one its end to the carrier and on the other endto the rotating levers having the capacity of moving angularly withrespect to the carrier;

the rotating levers would be made imbalanced, their center of gravitywould be displaced from their axles of rotation to a side according towhich its movement from the center to the periphery results in areduction in the variable-speed drive transmission ratio;

the pressure member would be made with the possibility of regulating thedependence of the force magnitude on movement, e.g., as power hydraulicor pneumatic cylinders;

the profiled surfaces would be made with the profile varying in theaxial direction and would be arranged with the possibility of theiraxial movement with respect to the pushers;

the profiled surfaces and the pushers may be arranged both at therotating levers and at certain parts of the mechanism for modificationof the transmission ratio and the pressure, which are connected to thelow-speed shaft.

The said features are essential and interrelated therebetween bycause-effect relation with the formation of a totality of essentialfeatures sufficient for achieving the technical result.

Namely, in a case the mechanism for modification of the transmissionratio and the pressure comprises the pressure members of the rotatinglevers (e.g., springs, hydraulic cylinders or pneumatic cylinders,etc.), it ensures their pressing to the direction of turning thatcorresponds to a decrease in the transmission ratio from the centralshaft to the low-speed shaft, the pushers and the guides profiledsurfaces may be arranged both at the rotating levers and at the memberconnected to the low-speed shaft; the said profiled surfaces are madehelical in the direction that ensures, if the carrier advances thelow-speed shaft in case of making the central shaft the driving one andmaking the low-speed shaft the driven one, an angular movement of therotating levers to the side corresponding to an increase of thevariable-speed drive transmission ratio; the profiled surfaces may bemade varying (non-flat) in the axial direction with the possibility oftheir angular movement with respect to the pushers; the center ofgravity of the rotating levers either may be at the axle of theirrotation (the levers are balanced) or may be displaced to the sideaccording to that its movement from the center to the periphery resultsin a decrease in the variable-speed drive transmission ratio; ifnecessary the mechanism for modification of the transmission ratio andthe pressure may be fixed while the variable-speed drive transmissionratio is maintained constant. In such a case both the said central shaftand the low-speed shaft may be either driving or driven, respectively.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a general diagram of the continuously variable transmission(Variant 1).

FIG. 2 is a general diagram of the continuously variable transmission(Variant 2).

FIG. 3 shows the arrangement of the pushers and the guides in thepositions (a) and (b).

FIG. 4 represents a variant of making a weight in the form of a shapedspring ring with alternating radial slots.

FIG. 5 is a plot showing the dependence of a force exerted by the powermembers made as disc springs on their axial movement (Variants 1 and 2).

The continuously variable transmission comprises the central shaft 1(FIGS. 1, 2) connected to the inner central friction discs 2 broughtinto contact with the intermediate friction discs 3, which are, in theirturn, brought into contact with the outer central friction discs 4attached to the epicycle 5 of the planetary variable-speed drive having,as its sun gear, the inner central friction discs 2 arranged on thecentral shaft 1, as well as the carrier 6. The intermediate frictiondiscs 3 are arranged on the axle 7. To ensure the optimal pressure ofthe central friction discs to the intermediate discs, the mechanism forcombined modification of the transmission ratio and the pressure isused.

According to the first variant of the invention (FIG. 1) the mechanismfor combined modification of the transmission ratio and the pressure ismade as follows.

On the central shaft 1 (FIG. 1) at both sides from the inner centralfriction discs 2 arranged with the possibility of axial movement thesupport members 9 are fixed both in the axial and in the angulardirections, to the said members 9 the stops 10 are attached that arebrought into contact with the power members applying an axial actionthat are made in the form of the plate springs 11 ensuring, depending ona movement, the positive, zero or negative rigidity. The circumferenceof the contact between the stops 10 and the springs 11 may have variousradii depending on the required force and deformation of the springs 11,including the radius that is maximally close to the radius of thecentral shaft 1. The springs 11, in their turn, are brought into contactwith the inner central friction discs 2 at the end that is rear relativeto the contact between the inner central friction discs 2 and theintermediate friction discs 3 arranged on the axles 7 that, in theirturn, are fixed in the bearings at the rotating levers 12 fixed with thepossibility of rotation on the carrier 6. The springs 11, in particular,may also have their bases in contact, e.g., not in their end positions,i.e., between the two inner friction discs 2. The support members 9 and15 between the two inner central friction discs may be made as a wholewith the common rear sides.

Similarly, the outer central friction discs 4, also having thepossibility of moving axially on the epicycle 5 along its innercylindrical surface, are pressed to the intermediate friction discs 3 bythe springs 13, e.g., plate ones, that are arranged with the possibilityof moving axially at their bases. The springs 13 are connected at theirbases by, e.g., pre-deformed members 14, e.g., tension springs, to thesupport members 15. The shoulders 16 are made on the support members 15in the area of fitting on the epicycle 5 and are arranged with thepossibility of contacting the springs 13. The springs 13 are fixed inthe axial and the angular directions on the epicycle 5 (which is, inthis case, stationary) and are in contact with the annular stops 17 madeon the support members 15. An embodiment is possible wherein the supportmembers 15 arranged between the two outer central friction discs 4 maycontact each other by their rear sides or may be made as a whole. Thestops 10 and 17 as well as the rear sides of the springs 11 and 13 actas the corresponding mechanical (kinematical) ties.

In one particular case the springs 11 and 13 may be made as one piecewith the inner and outer central friction discs, respectively, anddirectly act as the inner and outer central friction discs,respectively, the inner ones 2 and the outer ones 4. In such a caseraces are made on those springs on the same sides as on thecorresponding inner and outer central friction discs, as well as thecontact areas with the corresponding mechanical (kinematical) ties.

To ensure the adjustment of the pressure force depending on the speed ofrotation of the central shaft 1, the power members applying an axialaction of the mechanism for combined modification of the transmissionratio and the pressure are made as follows.

In one of the variants the power members applying an axial force aremade as the conical annular surfaces 18 arranged on the support members9 and directed toward the inner central friction discs 2 having the sameconical annular surfaces 20, in such a case between the inner and outerfriction discs 2 and the support members 9 the weights 21 are arrangedwith the possibility of their radial movement in the conical gap formedby the said surfaces 18 and 20 alongside with a radial movement of theintermediate friction discs 3. FIG. 4 represents an embodiment of theweight 21 in the form of a shaped spring ring with alternating radialslots 19 ensuring compliance of the springs in the circumferential andradial directions. The said conical gap may be also formed by the twoconical annular surfaces 20 on the rear sides, as facing each other, ofthe inner friction discs 2.

In another variant the power member applying an axial action is made asthe chamber 22 communicating with the source 23 of the pressurizedworking medium and arranged on the epicycle 5 with the possibility ofpressing at least one outer central friction disc 4 to the correspondingintermediate friction discs 3 with a force defined by the value of theworking medium pressure in the chamber 22.

The chamber 22 may be made with bellows (FIGS. 1, 2), the plate springs13—with holes for free passing of the pressurized working medium to theouter central friction discs 4.

According to the second variant (FIGS. 2, 3) of this invention themechanism for combined modification of the transmission ratio and thepressure is made as follows.

The axles 7 (FIG. 2) carrying the intermediate friction discs 3 arearranged through bearings on the rotating levers 12 connected to thecarrier 6 of the planetary variable-speed drive and carrying on thesides opposite to the intermediate friction 3 the counterbalances 24serving for balancing (partial or full) the rotating levers 12 andpushers 25 made, e.g., as rollers serving as the counterbalances andcontacting the guides made as the shaped surfaces 26 on the disc 27arranged on the low-speed shaft 8.

The low-speed shaft 8 is connected to the carrier 6 of thevariable-speed drive through a controlled mechanism, in particular, thecontrolled jaw clutch, one part 28 of which is arranged on the low-speedshaft 8 or on the disc 27 and the other part of the clutch is arrangedon the carrier 6.

In FIGS. 1 and 2 the intermediate friction discs 3, the axles 7 with thebearings, the rotating levers 9 with the counterbalances 24 and thepushers 25, as well as the guides are represented, for the sake ofsimplicity, in the singular; but there may be several of them, e.g.,six, which are arranged on the circumference with equal spacestherebetween.

The disc 27 is arranged on the low-speed shaft 8 with the possibility ofrotating relative to the carrier 6, the pusher 25 is connected throughthe spring 30, in this case this is a compression spring, to the carrier6 or the disc 27 (as shown in FIG. 3); thus the pusher 25 isspring-loaded to the side of angular movement of the rotating lever 12,corresponding to movement of the intermediate friction discs 3 towardthe center, which results in a decrease in the variable-speed drivetransmission ratio. Thus, when the pusher 25 moves under the action ofthe spring 30 from the position (b) to the position (a) (FIG. 3), i.e.,outwards, the end of the spring 30, which is connected to the disc 27,also moves from the position (b₁) to the position (a₁), and theintermediate discs 3 move from the position (b₂) to the position (a₂),i.e., toward the center (FIG. 3). Owing to this the transmission ratiofrom the central shaft 1 to the low-speed shaft 8 decreases.

The pushers 25 may be also attached to the opposite side of the rotatinglever 12. Then the tension springs 30 should, as it were, draw thepushers 25 toward the central shaft 1, which also results in a decreasein the transmission ratio. Sometimes, it is convenient to use, insteadof the springs 30, pneumatic or hydraulic cylinders connected, similarlyto the springs 30, to certain parts of the mechanism for modification ofthe transmission ratio and the pressure. In such cylinders thepressurized working medium is supplied according to any known method,e.g., from a receiver through a manifold (not shown in the Figures),with the pressure adjustment.

In all the above cases it is supposed that the carrier 6 rotates in thedirection of the arrow “w”, and the moment of resistance acts on thelow-speed shaft 8, and, consequently, on the disc 27 in the direction ofthe arrow “M” (FIG. 3).

A similar process occurs when torsion springs are used (not shown in theFigures) instead of the springs 30; such a spring should rotate the disc27 relative to the carrier 6 in the direction opposite to that of thearrow “M”.

The profiled surfaces 26 (FIG. 3) are made helical, therefore, when thedisc 27 is forced to rotate in the direction opposite to that of thearrow “M” with the carrier 6 stopped, in all cases the pushers 25 aremoved in the direction resulting in an angular movement of the rotatinglevers 12, what, like in the previous cases, reduces the transmissionratio. It is easy to note that deceleration of the low-speed shaft 8 andthe disc 27, when the central shaft 1 and, consequently, the carrier 6are rotating in the direction opposite to that of the arrow “M” (in thedirection of the arrow “w”) (FIG. 3), results in advancing the low-speedshaft and the disc 27 by the carrier 6, what, as in a case of loadingthe low-speed shaft 8 with the working torque, results in an increase ofthe variable-speed drive transmission ratio and decrease in the speed ofthe transportation means.

It should be noted that sometimes, proceeding from the arrangementconditions, it would be convenient to interchange the profiled surfacesand the pushers and to attach the pushers to the member connected to thelow-speed shaft 8, e.g., to the disc 27, and to make the profiledsurfaces 26 on the rotating shafts 12, e.g., on the counterbalances 24.But, the above-cited rule of action of forces and torques of thepressure members in different cases and the modification of thevariable-speed drive transmission ratio, as associated therewith,remains unchanged.

The profiled surfaces 26 may be made either helical flat or volumetric,i.e. with a profile varying along the axial direction, in order toensure the possibility of moving the pushers 25 along them in the axialdirection, i.e., with the variable-speed drive transmission ratioadjusted thereby.

In order to maintain the variable-speed drive transmission ratioconstant, it is necessary to lock the carrier 6 to the low-speed shaft8, i.e., to lock the transmission ratio modification controller. Forthis purpose it is necessary to include the controlled clutch 28-29,thereby connecting the carrier 6 to the low-speed shaft 8. The clutch 28-29 may be controlled manually or remotely, e.g., with a solenoid drive.

PREFERRED EMBODIMENT OF INVENTION

At the minimum variable-speed drive transmission ratio that in respectof, e.g., a car is 1.2-1.3, the intermediate friction discs 3, asarranged at the axles 7, are in their central position (the lowestposition in FIG. 1). The deformation of the plate compression springs 11is the greatest due to the maximal axial separation of the inner centralfriction discs 2 under the holding-apart action of the intermediatefriction discs 3 brought in contact in this position at their maximumthickness with the inner central friction discs 2 and due to the contactof the springs 11 with the ties—stops 10 at the support members 9. It isknown that plate springs, with their small thickness and highdeformation values, have negative rigidity, and this parameter dependson the size of the spring 11 and on the position of the stops 10. Thedependence of the rigidity of the springs 11 on their size and axialdeformations is described, e.g., in the book by Birger et al. StrengthAnalysis of Machine Parts, Moscow, Mashinostroyenie. 1979, pp. 171-172.

The required pressure of the springs 11 in this position is low due to ahigh value of the friction coefficient conditioned by high pressures anda small thickness of the oil film at an almost constant torque, which isensured by the specification of the springs 11. At the outer centralfriction discs 4, where their separation is small due to the smallthickness of the intermediate friction discs 3, the deformation of thespring 19 is not large, the stops 17 do not touch the springs 13 yet,and the pressure force at this point of contact, when transmissionratios are the lowest, is minimal, in spite of a low value of thefriction coefficient. This is depicted in the plot represented in FIG.5, the left side. (On the abscissa axis the axial movement in thedirection of the arrow increases for the outer springs 13 and decreasesfor the inner springs 11.)

When the axles 7 and the intermediate friction discs 3 are moved to theperiphery (up in FIG. 1) the transmission ratio increases, thedeformation of the springs 11 decreases, the friction coefficient on theinner central friction discs 2 becomes lower due to lowering of thecontact stresses and thickening of the oil film, what requires toincrease the pressure of the springs 11, and this is ensured by theircharacteristics. Due to an increase in the deformation of the springs13, they are brought into contact with the stops 17 and, while incontact, increase their rigidity, what progressively increases theirpressure on the outer central friction discs 4. Such a pressure is justnecessary in the mechanism due to increase of the transmission ratio andan associated increase in the torque at the epicycle 5, i.e., at theouter central friction discs also, though the friction coefficientincreases at that point of contact. The required pressure in ensured bythe parameters of the springs 13 and the stops 17 (see the above-citedpublication, pp. 462-473); this is depicted in the plot represented inFIG. 2, the middle part.

At the maximum transmission ratio, i.e. in the peripheral position (theupper position in FIG. 1) of the intermediate friction discs 3 (FIG. 3)and the axles 7 the friction coefficient on the outer central frictiondiscs 4 is at the maximum, and the required torque at the low-speed 8 isusually limited, e.g., due to wheel-spin. Therefore, the requiredpressure force of the springs 13 is limited, what is just ensured bypre-deformed members 14 (e.g., by rigid tension springs, etc.), which donot allow the pressure force to exceed a definite value due to thedetachment of the bases of the springs 13 from the shoulders 16 of thesupport members 15, earlier pressed to each other by the tie of thisgroup of resilient power members—the springs 14.

At the contact of the inner friction discs 2 with the intermediatefriction discs 3, due to further lowering of the friction coefficientand mainly due to lowering of the required torque, e.g., in wheel-slip,the need in an increased pressure force is reduced, what is ensured bythe springs 11 having small deformation in the area of positive rigidity(FIG. 5, the right side of the plot).

Thus, the required pressure at the points of contact is ensured by theparameters of the springs and the ties as well as by modification of thevariable-speed drive transmission ratio. This is the essence of thecombined modification of the transmission ratio and the pressure. Also,the friction coefficients in all areas of contact at all positionsdecrease when the speed of rotation increases. This results in the needto increase the pressure that, at low speeds of rotation, raises to some“overpressure” and results in an insignificant reduction of theefficiency.

Therefore, both at the inner friction discs 2 and at the outer frictiondiscs 4 pressure members may be used, which act as adjusters increasingthe pressure force.

Thus, for example, when the central shaft 1 rotates at an increasedspeed, the weights 21 tend to go to the periphery, creating thereby anadditional pressure on the inner central friction discs 2, and the formof the conical surfaces 18 and 20 as well as the weights 21 enables toattain the necessary values of the pressure force, depending on thespeed of rotation and the radial movement of the weights 21. The radialmovement of the weights 21 is eased by their compliance in thecircumferential and the radial directions due to the availability of theslots 19.

The outer, connected to the epicycle 5, springs 13 and the supportmembers 15 do not rotate, therefore the pressure force may be adjusted(increased) by supplying the pressurized working medium (gas, liquid) tothe chambers 22 from the source 23, which is determined, e.g., by therotational speed transducer of the central shaft 1 and the movementvalue of the axle 7, i.e., by the transmission ratio.

The torque from all the springs, the stops, the support members etc. istransmitted, like in similar mechanisms, to the friction discs by thefriction force, since the friction coefficients of rest at friction ofboundary (incomplete) lubrication are several times higher than thefriction coefficient in an oil film when working surfaces are rolling;in such a case the pressure forces are equal and the radii are far lessdifferent than the friction coefficients. Also, the said friction ofrest contacts are good protective members of the mechanism in cases ofunexpected seizure of the variable-speed drive due to breakage of parts,entering of unlocked fastening members into the mechanism etc.

The second variant of the invention is implemented as follows. Thecentral shaft 1 (FIGS. 2, 3) is rotated, e.g., by the engine of atransportation means at the almost constant torque. Here the mechanismof combined modification of the transmission ratio operates as follows,While the load (moment of resistance) at the low-speed shaft 8 is small,the action of the pressure members (springs, cylinders) prevails, andthe rotating levers 12 are in the position corresponding to the minimumratio of transmission from the central shaft 1 to the low-speed shaft 8.For example, when the epicycle 5 of the planetary variable-speed driveis stalled, the inner central friction discs 2 are most close to therotation axis of the central shaft 1 and the low-speed shaft 8, theinner central friction discs 2 are brought into contact with theintermediate friction discs 3 along the small radius of the latter andthe outer central friction discs 4 —along the greatest radius (the realminimum transmission ratio is about 1.2-1.3).

With an increase of the moment of resistance at the low-speed shaft 8the pushers 25 begin, overriding the action of the static pressuremembers, e.g., the spring 30 (FIGS. 2, 3), moving along the profiledsurfaces 26, thus shifting the rotating levers 12 to a positioncorresponding to the increase in the variable-speed drive transmissionratio. At the maximum moment of resistance the pushers 25 come to theend of the profiled surfaces 26, and the pressure power member, inparticular the spring 30, is deformed completely. The intermediatefriction discs 3 are in the position, which is at the maximum distancefrom the central shaft 1, and this corresponds, when the epicycle 5 isstalled, to the maximum transmission ratio of the variable-speed drive(the real maximum transmission ratio is from 6 to 11). It should benoted that if the central shaft 1 is decelerated and the rotationalaction of the engine is transmitted to the epicycle 5, which is allowedaccording to the planetary systems, the above-stated principle of actionof the mechanism for modification of the transmission ratio and thepressure remains the same, with the exception that the intermediatefriction discs 3 at the maximum transmission ratio are brought close tothe central shaft and at the minimum one are brought to the maximumdistance therefrom, i.e., their position is inverse to that describedabove.

When the moment of resistance decreases, the process inverse to thatdescribed above occurs at the low-speed shaft 8, and the variable-speeddrive transmission ratio reduces again. Thus, the “rigid” characteristicof the engine of a transportation means become “soft” that is typical,e.g., for a DC motor with series excitation or combined excitation, orfor a drive with a torque converter.

When the profiled surfaces 26 are volumetric and the pushers 25 moveaxially relative to them, the mechanical characteristic at the low-speedshaft 8 becomes adjustable by axial movement of the pushers 25 relativeto the profiled surfaces 26.

In a case of using the adjustable pressure members, e.g., pneumaticcylinders instead of the tension-compression springs 30, wherepressurized gas (air) is supplied under control, e.g., from a stationaryreceiver through a pressure regulator and a manifold ensuring the supplyof pressurized gas from a stationary piping to rotating cylinders, themechanical characteristic at the low-speed shaft 8 also becomesadjustable.

In a case where it is necessary to lock the mechanism for combinedmodification of the transmission ratio and the pressure as well as thevalue of pressing the inner 2 and the outer 4 central friction discs tothe intermediate friction discs 3 in any position and, consequently, tofix the transmission ratio, the clutch 28-29, e.g., a jaw one, isengaged, interlocking the carrier 6 and the low-speed shaft 8.

In a case of partial balancing of the rotating levers 12 with thecounterbalances 24 the rotation of the levers 12 due to their imbalance,when the carrier 6 rotates, should be in the same direction as under theaction of the pressure member, e.g., the spring 30. Then, such partialimbalance at low transmission ratios of the variable-speed drive and,consequently, high speeds of rotation of the carrier 6 may eithercontribute to the action of the pressure members or, at the same forces,reduce their dimensions and weight. And, in a case of, for example, thedriving central shaft 1, the center of gravity of the rotating lever 12should be displaced toward the counterbalance 24; but in a case of thedriving epicycle 5 it should be displaced toward the intermediatefriction discs 3, i.e., to the side where its movement from the centerto the periphery results in reducing the transmission ratio of thevariable-speed drive.

INDUSTRIAL APPLICABILITY

The utilization of this invention enables to create a continuouslyvariable transmission having a high efficiency, higher reliability andaccuracy of control over regulating the transmission ratio in conditionsof varying load at the low-speed shaft due to providing it with a stableloading mechanism for modification of the transmission ratio and thepressure.

What is claimed is:
 1. A continuously variable transmission comprising aplanetary friction variable-speed drive consisting of central inner andouter friction discs arranged, respectively, on a central shaft and onan epicycle and laterally embracing intermediate friction discs, amechanism for combined modification of the transmission ratio and of thepressure made in the form of rotating levers carrying the intermediatefriction discs and arranged on a planetary variable-speed drive carrier,which is connected to a low-speed shaft, with the possibility ofchanging the position of the rotating levers, characterized in that themechanism for combined modification of the transmission ratio and of thepressure is provided with power members applying an axial action, whichare arranged on end sides of all the said central friction discs so asto ensure the contact of the said members in annular areas of thecentral friction discs, said areas being opposite to annular areas ofcontact between the said friction discs and the intermediate frictiondiscs, the average axial rigidity of the power members applying an axialaction, which are brought into contact with the central outer frictiondiscs, being made so as to be higher, in terms of absolute value, thanthe average rigidity of the power members applying an axial action,which are brought into contact with the central inner friction discs. 2.A transmission according to claim 1, characterized in that the mechanismfor combined modification of the transmission ratio and of the pressureis provided with support members arranged on the central shaft and onthe epicycle from a rear side of the power members applying an axialaction and being made with stops contacting the power members applyingan axial action with the possibility of varying the axial rigidity ofthe latter both in magnitude and in negative/positive value.
 3. Atransmission according to claim 1, characterized in that the powermember applying an axial action is made as a chamber connected to asource of a pressurized working medium and arranged on the epicycle withthe possibility of pressing at least one central outer friction disc tothe respective intermediate friction discs, depending on the pressure ofthe working medium in the said chamber.
 4. A transmission according toclaim 1, characterized in that the said power member applying an axialaction is made as an annular conical surface made on a support member,which is arranged on the central shaft, and directed toward the innercentral friction disc with an annular conical surface made thereon,between the latter and the said annular conical surface of the supportmember are weights being arranged with the possibility of their radialmovements along a conical gap formed between the annular conicalsurfaces and of variation of the force of pressing the inner centralfriction discs to the intermediate friction discs.
 5. A transmissionaccording to claim 1, characterized in that the power member applying anaxial action is made as annular conical surfaces made on rear sides,which face each other, of the inner central friction discs, between thesaid annular conical surfaces are weights being arranged with thepossibility of their radial movements along a conical gap and ofvariation of the force of pressing the inner central friction discs tothe intermediate friction discs.
 6. A transmission according to claim 4,characterized in that the said weights are made as shaped spring ringswith alternating radial slots.
 7. A continuously variable transmissioncomprising a planetary friction variable-speed drive consisting of innerand outer central friction discs arranged, respectively, on a centralshaft and on an epicycle and laterally embracing intermediate discs, amechanism for combined modification of the transmission ratio and of thepressure made in the form of rotating levers carrying the intermediatefriction discs and arranged on a planetary variable-speed drive carrier,which is connected to a low-speed shaft, with the possibility ofchanging the position of the rotating levers, the mechanism for combinedmodification of the transmission ratio and of the pressure being madewith pushers arranged with the possibility of moving along guides,characterized in that the mechanism for combined modification of thetransmission ratio and of the pressure is provided with members applyingpressure to the rotating levers and power members applying an axialaction, which are arranged on end sides of all the said central frictiondiscs so as to ensure their contact in annular areas of the centralfriction discs, said areas being opposite to annular areas of contactbetween the said friction discs and the intermediate friction discs, theaverage axial rigidity of the power members applying an axial action,which are brought into contact with the outer central friction discs,being made so as to be higher, in terms of absolute value, than theaverage rigidity of the power members applying an axial action, whichare brought into contact with the central inner friction discs, themembers applying pressure being connected to the rotating levers withthe possibility of ensuring rotation of the said levers to a sidecorresponding to reduction in the ratio of transmission from the centralshaft to the low-speed shaft.
 8. A transmission according to claim 7,characterized in that it is provided with a controlled locking mechanismconnected, respectively, to the carrier and the low-speed shaft.
 9. Atransmission according to claim 7, characterized in that the controlledlocking mechanism is made as a controlled jaw clutch.
 10. A transmissionaccording to claim 7, characterized in that the guides are made asprofiled surfaces arranged helically, which direction ensures, in caseof making the central shaft the driving one and advancing by the carrierthe low-speed shaft made the driven one, an angular movement of therotating levers to the side corresponding to an increase in the ratio oftransmission from the central shaft to the low-speed shaft.
 11. Atransmission according to claim 7, characterized in that the memberapplying pressure to the rotating levers is made as at least one springconnected on one of its end to the carrier and on its other end to thelow-speed shaft, with the possibility of their angular movement relativeto each other.
 12. A transmission according to claim 7, characterized inthat the member applying pressure to the rotating levers is made as atleast one spring connected on one of its end to the low-speed shaft andon its other end to a rotating lever with the possibility of its angularmovement relative to the carrier.
 13. A transmission according to claim7, characterized in that the member applying pressure to the rotatinglevers is made as at least one spring connected on one of its end to thecarrier and on its other end to a rotating lever with the possibility ofits angular movement relative to the carrier.
 14. A transmissionaccording to claim 7, characterized in that the rotating levers are madeimbalanced, their center of gravity being displaced from their axes ofrotation to the side in accordance to which its movement from the centerto the periphery results in a decrease in the ratio of transmission fromthe central shaft to the low-speed shaft.
 15. A transmission accordingto claim 7, characterized in that the member applying pressure is madewith adjustable dependence of the force on movement as power cylindersconnected to a source of a pressurized working medium.
 16. Atransmission according to claim 10, characterized in that the profiledsurfaces are made with the profile varying in the axial direction andarranged with the possibility of their axial movement relative to thepushers.